1. Field of the Invention
The invention generally relates to whipstock mechanisms for use in drilling subterranean wells, and more particularly, relates to a whipstock device and an anchor for the whipstock, which anchor may be run into the wellbore with the well casing and allows for select setting and orientation of the whipstock downhole and for retrieval of the whipstock, as desired. The invention includes both the apparatus and method of operation.
2. Description of the Related Art
Whipstocks are commonly known and used equipment in the drilling of subterranean petroleum wells. A whipstock is a device which is positioned downhole within a wellbore to change the direction of the drilling bit. Whipstocks are often used in instances in which particular wellbore direction is desired, to direct the drill bit during drilling operations. The whipstock is placed in the wellbore at a desired location where a whipstock anchor retains and prevents downward movement of the whipstock. Drilling while employing a whipstock has been commonly referred to as directional drilling because the whipstock causes the drill bit to be directed in a desired direction causing the wellbore path to deviate in a desired configuration.
It is very important in drilling subterranean wells to obtain a well hole particularly directed along a desired path. Direction of the well hole is often of utmost importance, in particular, in the case of subterranean petroleum wells. Petroleum (i.e. oil and natural gas) is often found in very unsymmetrically shaped subsurface formations. Only if a petroleum well hole is directed into specific locations within the surface formations will the well be successful for producing petroleum from the formation.
In addition to advantages of directing well holes into specific subsurface formations, it is often advantageous to have the capability to selectively cause a well hole to deviate in its subterranean path. Deviation of the well hole is important, for example, in many of the newer well drilling practices, such as horizontal drilling. In horizontal drilling, a vertical wellbore is drilled to a desired subsurface level, at which level the wellbore is directed generally horizontally through a subsurface formation. Many other diversely configured wellbore arrangements are desired for particular applications due to differing sedimentary properties and desired well production arrangements.
As previously mentioned, whipstocks have been employed in the past to cause the direction of wellbore drilling to deviate in desired directions. In those applications, a whipstock has typically been located within a wellbore at a desired location and permanently affixed there within the wellbore. Whipstocks have been fixed within the wellbore by a packer means or some other means for wedging the devices for securement at the desired locations. The prior art whipstock mechanisms have at least two significant problems. First, the prior art whipstocks are typically not easily selectively oriented. Second, the prior art whipstocks have not generally been easily retrievable from within the wellbore.
Orientation of the prior art whipstocks is a problem because it is hard, if not impossible, to selectively fix and/or detect orientation of the whipstock when located and secured downhole within a wellbore. A number of prior art means have been employed to orient whipstocks. These means include radioactive detection means or a gyroscope type means. Those prior art means for orienting a whipstock typically have been employed to orient the whipstock device in a permanent packer located in the wellbore. In those arrangements, the whipstock is secured with the permanent packer within the wellbore. The orientation of the whipstock is, thus, dictated by the placement and orientation of the packer. Select packer orientation has been hard, if not impossible, to achieve in the prior art devices. This is because the packer must be manipulated from the surface, generally very remote from the packer location downhole, to the desired orientation. Accuracy of the orientation is, therefore, generally limited. Though the prior art means have achieved some degree of orientation accuracy of whipstocks, greater accuracy is desired. Additionally, only a single orientation of the prior art whipstock device is possible at each packer location because a single orientation is set at the outset by design of the whipstock and packer mechanisms. Even further, orienting a whipstock in these prior art manners is complicated by the fact that these orienting means and packers often become lodged in the wellbore other than as desired. Orientation of the prior art whipstocks, due to the operations and configurations of the prior art orienting means, is, thus, quite problematic.
As for retrieval, the prior art whipstock orienting means and the prior art whipstocks have typically not been retrievable once placed and secured within a wellbore. Previously, a whipstock has been set within the wellbore on what is referred to as a permanent packer. In locating and securing the whipstock downhole in a wellbore, the permanent packer is first set. The whipstock is then run into a receptacle therefor incorporated with the permanent packer. The permanent packer typically has been set in an orientation detected from the surface. Such a permanent packer is not easily retrievable from the wellbore, so retrieval of the whipstock and other manipulations thereof are complicated.
The present invention is an orienting, retrievable whipstock anchor which allows a whipstock to be selectively located and oriented within a wellbore. The invention provides quite accurate location and orientation of the whipstock, and so overcomes the problems with the prior art operations and equipment for whipstock orientation downhole in a wellbore. Additionally, the invention allows for retrieval and resetting of the whipstock, as desired. Because the prior art whipstock devices have not overcome these problems of orientation and retrieval, the present invention which overcomes these problems is a significant improvement in the technology and art.